Color-selective optical system



J. E. ALERIGHT coLowsELEcTn/E OPTICAL SYSTEM March 16, 19,54

2 Sheets-Sheet 1 Filed Oct. 19, 1950 lNyENTOR WQA TTORNEY l il March 16, 1954 J. E. ALBRIGHT COLOR-SELECTIVEOPTICAL SYSTEM 2 Sheets-Sheet 2 Filed Oct.' 19, 1950 Patented Mar. 16, 1954 COLOR-SELECTIVE OPTICAL SYSTEM James E. Albright, Haddon Township, Camden County, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application October 19, 1950, Serial No. 191,068

19 Claims.

This invention relates to color television systems. It has particular reference to an optical system for selectively combining a plurality of component color vimages in substantially exact registration.

In many types of color television systems, the different component color images are separately reproduced. In order to make a, composite image it is necessary to employ an optical system suitable to effectively superimpose the different component color images. The superimposition of the component color images must he effected in sufficiently good optical registration that the composite image may have the appearance of the original subject.

One optical system which has been employed quite successfully for such a purpose includes one or more color-selective devices which are known as dichroic reflectors. Such apparatus has the property of reflecting light of a predetermined color and, at the same time, of transmitting without substantial modification light of a different color. Representative examples of dichroic reflectors are disclosed in two U. S. patents to Glenn L. Dimmick. These are 2,379,790, granted July 3, 1945, and titled Dichroic Reflectors and 2,412,496, granted December 10, 1946, and titled "Color Selective Reflector.

Essentially a dichroic reflector, of the type shown in the two Dimmick patents referred to,

consists of a transparent support upon which is mounted a color-selective layer. This layer is a reflector for light of a selected color and is essentially transparent to light of non-selected colors.

Heretofore in color television systems using dichroic reflectors, each of the reflectors has been arranged in such a manner that one surface of the transparent support is provided with the color-selective reflective layer. The layer has been located on that surface of the support which is nearest to the source of light of the color to be reflected. As a result, the light to be reflected did not have to traverse the transparent support. However, the colored light which was to be transmitted through the reflective layer did have to pass through the transparent support.

Systems of this character, as used previously, have been effective to combine the different component color images in reasonably good registration so long as relatively small viewing angles were used. In general, such systems are satisfactory for viewing angles which do not exceed plus or minus five degrees from a central position. The registration of a combined color television image is not entirely satisfactory for any greater viewing angles.

Accordingly, it is an object of this invention to provide an improved, wide angle optical system having one or more color-selective com-n ponents and in which good registration of the component color images is effected.

Another object of the invention is to provide an improved arrangement of dichroic reflectors whereby to effect good registration of a plurality of component color images at relatively wide angles of view.

Still another object of the invention is to provide an improved wide angle optical system comprising one or more dichroic reflectors for use in an image-reproducing color television system.

In accordance with the present invention, the improved arrangement of dichroic reflectors is one which produces light paths between the respective sources of the component color images and a predetermined plane which are substantially identical in length and character. All of the colored light is required to travel partly through air and partly through glass, or other transparent medium having an index of refraction different from that of air. The arrangement of the dichroic reflectors is such that light of all colors is required to travel through equal distances in air and in higher refractive media. In general, this beneficial result is obtained by disposing one or more of the dichroic reflectors so that the color-reflective layer is separated from the source of the light which it is to reflect by a polychromatic light-transmitting member. In this way the reected, as well as the transmitted, light is required to traverse the transparent member. Such an arrangement effectively equallacs the length and character of the paths of the reflected light and the light transmitted by the dichroic reflector.

yThe novel features that are considered charac-l teristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings.

In the drawings;

Figure l is an embodiment of the color-selective optical system in accordance with this invention for a directly viewed television reproducing apparatus;

Figure 2 is a fragmentary view, to an enlarged scale, of the dichroic refiectors of Figure 1, illustrating the manner in which the present invention operates;

Figure 3 is another embodiment of the invention in a projection type of television imagereproducing system;

Figure 4 shows another embodiment of the invention in a directly viewed television imagereproducing" apparatus;

Figure" 5 slo'ws `still another modified form of the invention adapted for use in a directly viewed television image-reproducing apparatus; and

Figure 6 shows an embodimentl of` the invention for direct viewing in which one of the dichroic elements is dual-reflective.

Reference rst will be made to Figure l ofthe drawings. rllhe three sources of differently colcred image-representative light are shown asred, blue and green kinescopes II, I2 and I3 respectively. Since the apparatus required to produce the different component` color images upon the lunesccpes forms no part of the present inv-em tion and may be conventional, it has not been strewn. rIt will be vruidinstood nevertheless-that, upon the respective luminescent screens of the kinescopes' M, IZ-a-nd I3 there are produced, substntially ic'onculrrently,` red, blue .and green cocnponent color television .'Ilewpai'tial television image formed on the screen of tlierdkinesoope II isdirected so that itis intercepted by a dichroic reflector I4. 'As in 'the two- Dimmick patents referred to, the dichroic reflector I4 comprises 'a substantially ytramrparentv support i5 upon one surface of which is-formed a redireflective vlayer ior lcoartiiig: I0. Blue and vgreen light is transmitted by this coating Without substantial modification. 'I'le support I'Smay lne oi' glass or other suitable transparent material such as a `good grade of clear ijlasticfsubstance. Inf any case, it will be ncted'that-the red'reflectivecoating I6 is formed on that surface-of the support I=5 which is remote thefred kinescope II. Such `an arrangement'is `'oneoi the features of the present inven- Previously, the colored light-reflective coating has been -formed on the surface `of the support which is adjacent to the source 'of the light to be reflected. In the present instance, thesurface of support I5 which is closest tothe kinescope fII yis treated so that 4itis non-reflective. For `example, this surface may be treated as taught in U. xS: 4Patent 2,397,929, granted April 4, A1946, to-G. L; `Dimmickand titled Reduction in Reflection from Glass. Also, as usually arranged,.'thefdlchroic re-iiector I4 is disposedisubstantially at 45 degrees relative to the face of the redkinescopelli.

Also,associated with the blue and .green .kinescopes `l2 and 153/, `there is provided another dichroic-reiiector I1. In thiscase, a blue-reflective coating I8 is provided between `a pair of transparent `optical 4members. or `supports `I9. and 20. The outside r.surfaces of the members I9 and 2li` are treated so as vto render them `non-reflective. In accordance with this invention, the'tot'al thickness of thedichrcic reflector I'I is substantially equal-tothe total` thickness of the dichroicreec tor I4. blue kinescope vl'2 is `mounted in relation to the dichroic reflector vI'I similarly to th'e manner in which the red kinescope II is arranged `with respect to the dichroic reflector I4. The-greenki-nescope I3 is mounted substantially vertically, as shown, so `that it is in `alignment with both of the dichroic reflectors I4 and I1.

In Lbrder that the flight images `of different @alors man rtnethreemnespes u, mandlsmay be superimposed for observation, there is provided a plane mirror or reflector 2l mounted substantially in alignment with the dichroic `refiectors I4 and I1.

In general, the optical system as described functions somewhat similarly to those previously used. The dichroic reflector I4 reflects upwardly, asfviewcd in the drawing, the red lkht` derived fromv the kinescope I I. This reflectoralso transmits upwardly toward the mirror 22 without substantial modiiication, blue and green light respectively froxnkinescopes I2 and I3. The blueselective dichroic reflector I1 functions to reflect bluey licht derived from the kinescope I2 so that it is directed upwardly. Also, the dichroic re- |1 transmits, without substantial modification green. light derived from the kinescope I3. Accordingly, an observer looking into the mirror 2l isl'alileto see the three partial images in red, blue and green colors produced by the kinescopes II., I2 vand I3, respectively. Furthermore. by suitably positioning the optical components including` the dichroic reectcrs .I4 and Il with` respect to the kinescopes, the three colored images. may be seen substantially in good optical registration with one another.

One `of the requirements `for registering the three colored images is that the different light paths from the respective `kinescope screens to the observer be substantially equal in length. `In general, this requirement may be met by mounting the kinescopes Aat suitably. different distances from lthe dichroic reflectors. Suchen arrangement is Well known to those skilled in -theart However, such an arrangement is capable v.of providing substantially goodregistration of the lthree component color .images only if viewed Within` a comparatively small angle of `.the order of magnitude of `plus or minus five degrees from a central position. The present invention, however, takes into account, not only the equalization of the length of the light paths from the `diierent'kinescopes but also the equalization of the thicknesses of the different media through which the light travels in the different paths. By making these factors substantially identical for all of the light paths, in accordance with .this invention, the component color images .may be viewed from substantially any angle. Moreover substantially exact optical registration of these images will'be eiected.

For a more detailedexplanation of the'manner in which this Afeature of the invention is accomplished, reference now will be made to Figure 2.

Fragmentary cross-sectional portions ofthe red and blue selective dichroic reflectors I4 and Il. respectively, are shown to a considerably enlarged scale. 'For the purpose of this description only one point on `the diierent kinescope screens will be considered. Corresponding points on Vthe'three kinescopes have ,been chosen. These are designated. as points R, B and G,A located respectively on the screens of the red, blue and green kinescopes II, I2 and I3. Two paths of light from each ofthe points vare traced. These `two 'light paths are representative 'oi dinerent'angles from which the reproducing apparatus may be viewed. Itis not intended that the'twopaths chosen'ror illustration Aare the limiting angles 'of view, but merely asrepresenta'tive of the manner in which the ,present invention operates.

From a iirst .angle of view, the .path of light from 4theredpoint R is .represented by .the .onen arrcwfheadszsuchas 22h11 theiulllines. ,It `will beseen .that the .red light ,pathy .intersects non-reflecting surface of the dichroic reflector support I5 at a point 23. In accordance with the index of refraction of the support, the light path is altered as it traverses the support so that it impinges upon the red-reflective coating I6 at a point 24. The red light is reflected and emerges from the dichroic reflector support I5 at a point 25. It is to be noted that the red light path traverses the support I5 twice.

Consider now the path of light from the blue point B. From the assumed angle of View, this light path is represented by the solid arrow heads such as 26 on the full lines. The blue light path intersects the non-reilecting surface of the support I9 at a point 21. The direction of the light path is changed through the denser medium of the support so that it impinges upon the bluereflective coating I8 at a point 28. The blue light is reflected and emerges from the dichroic reflector support I9 at a point 29 and continues generally upwardly to intersect the blue dichroic reflector I4 at the point 24. It then follows the same path as the light from the red point R, finally emerging from the dichroic reflector I4 at the point 25.

Similarly, the light path from the green point G is represented by the half-solid arrow heads such as 3l on the full lines. The green light path intersects the non-reiiecting surface of the support 20 at a point 32. The direction of the green light path is changed through the denser medium of the support so that it intersects the blue-reflective coating I8 at the point 28. It then follows the same path as the blue and red light, nally emerging from the dichroic reflector I4 at the point 25.

Inasmuch as the points R, B and G are representative of all other points on the screens of the red, blue and green kinescopes II, I2 and I3, respectively, it will be appreciated that the three component color images will be viewed siniultaneously and in substantially exact optical registration.

As illustrative of another angle of View, the paths of light from the selected points R. B and G are represented by the broken lines emanating from these points. Different colors of ythe light in the different portions of these paths again are represented by the different arrow heads. Without tracing in detail each of the representative paths of light from the three different sources it may be seen that they all emerge finally from the dichroic reector I4, at a point 33. Also, it will be noted that, again, the light from the three different sources is in substantially exact optical registration.

The registration of the three color images' from substantially any angle of view is effected in accordance with the present invention by the proper arrangement of the dichroic reflectors relative to the observer and to the kinescopes. If the thickness of the support I5 of the dichroic reflector I4 is represented as T, then the thickness of the supports I9 and 2| of the dichroic reflector I1 each should be substantially equal to Such structural parameters, together with the described disposition of the color-selective coatings on the supports relative to the sources of light, are the essential features of the present invention by which the Wide vangle, optical registration of the images is secured.

The light path from the red point R, for example. includes a portion through a medium which is more dense than air. This medium comprises the support I5 of the dichroic reector I4. It will be noted that the red light twice traverses the support I5 of thickness T. Also, the light path from the point R. makes an angle A with the normal to the support surface at point 23. Since the support I5 is a light-transmitting medium having a density greater than air, the red light path is altered through the support I5, making an angle B with a normal to the surface of the support. If N is the index of a fraction of the support I5, then sin A N Also, the path of red light after reflection by the coating IB at the point 24 makes an angle B with the normal. Consequently, the distance traveled through the support I5 between the entrance point 23 and the emergence point 25 is equal substantially to 2T i COS B Consider now the path through the dichroic reflector I1 of the blue light from the point B. It intersects the surface of the dichroic reflector support I9 at the point 21 at substantially the same angle as the red light previously described. In this case, however, the blue-reflective coating I8 is located between the supports I9 and sin B= 20. The thickness of each of these supports is equal substantially to Consequently, it is seen that the total length of the blue light path through the supports I9 and I5 is equal substantially to cos B This corresponds with the length of the red light path through the dichroic support I5.

In substantially the same manner it may be seen that the light from the green point G, in traversing the supports I9 and 2l of the dichroic reflector I1, has a length equal substantially to cos B The length of the green path, between the entrance and the emergence points of the red dichroc support also is equal to cos B Y The total distance of the green light path through made substantially equal. `The lengths of'the different lightY paths in air may be equalied in the usualnianner, Accordingly, it is 'seien that, not only are the dihierent light paths equalicedvin length, but also the distances traveled in the different media are equalized. Accordingly, proper optical registration of the'three component color images rhey be efleeied ler eirleeiehllelly eey allele le, ehewh er1 arrangement ef sliehrele relleeferlelfh f' eeeerrlerree with the. Ilreeehi lhye'riilerr. whieh may be used advantageously a projection tylsi'e of a television image-reproducing system. In this case, the red, blue and green knescopes I I, I2 and I3, respectively, are aigrjai'lgec substantially at righi ehgleehe ehe another ee ellewrl- The Kiheseioees H, '.2 ehe le ere prehsleewhh heheh hreieetlerl Systeme represented et 3.4, @l erll'rlli resheetiyelyli will he hhslereleed their.' the Plieieeiierr `systems 'dlhererhrhetleelly Shown herein mey be ef any desired. tyhe For .exemple e re- `'lecltive type o f system such as the igvellknown Schmidt system rhey'he erhpleyed .edyehieeeeuely- The projection systems direct thelight from their associated kinescopes to an 'arrangement of crossed dich-rolo reflectors 31 and 38. The dichroic reflector 31, for example, may consist of transparent ,euphorie ,3e ehe @l between which there le provider-d. e red-refleetlye eeeilhe vThe diehroie .refleeier il may he Substantially of .the seme seherel character he the relleeielr Il 0f Figures 1 and 2. The dichrgi ,-le'Q ,3..8 559m' prises a pair of transparent supports 43 and 44 between which there is provided a blue-reilective coating 45. The reilector 38 also may be of the same general character as the reflector I1. In

-this case, however, it isma'de into parts mounted respectively on opposite sides of the reflector l31. The light derivedfrom the crossed dichroic reilectors 31 and 38 is directed onto the plane refleeting mirror 2I and thence to a viewing screen 46. The outside surfaces of the transparent suppoetsch, 4I, 43 and k4,4 are meliehOh-reective- In general, the operation of the ycrossed di chroic reliector system is similar y.those pregi' viously used. 'I'he red light; derived from the kinescope II is reilected by the coating 42 of the dlchroic reflector 31. `-Blue and green lights are transmitted Without ehbeielltilll .lllpfllleellell thl'elleh lhedlehrelerelleeler 3l? llllellehl ,def

fl'ectors 31 and Siembodies'the presentinfvent' n. A

The light-reflective coating vis located 'substa'n tially at the center of each of the reflectors. In this way the light; Whiclris reflected, as well as they irerlemltierlr hy. eeeh-9lihefilghrsle provide eachof the supports I9V anLZI with frehreeey Ahilt. eleerieihe yyhleh "ere ehh-e -hilelly identical in thecharacter of the `media tra lise@ It Will appreciatedthat thedichroic nijlcctor I4 of Figure 1, in itself, is not ,thesubstanceoi the present levehileri 'gerhelilerly les heed l.. the crier ,eri- A-e, rrevleirely heed; this. reileelereerr: 'ventionally is mounted with the cclohselectiye ,reflechir-e ,eeerllne 16 eslieeerlt le fille Ieewree freie whleh `the light fe he ,reflected le .qerlverl "'lhgee .eerde'llee with .this lhy-ehileh. the refletter.y 1.4 .le inverted to place` this' coating'reniote' 'frm light sehree. However! the illehrele -refleetir- 'lll is, of Aa somewhat special character. It may formed in two general steps. lnlthe rstfs'tep,

either the support 'I9 or 2141s' prccessedtc'iiec'eive i the' color-reflective coating I8,` inthe usu` lway. In the second step, the vother One `of the's'upports is cemented` or otherwise suitably bon'cgLtQ. e reneetive vcc'iatmg is; It is necessary.' cicbursegtl a thickness equal `surstcntiany to `@rif-irri1i ,r'xh thickness yof vthe support 15' of `the diclrqic `rey flector I4. l

In case that it is not `desired to einploy, a di; chroic reflector of the type corresponding to the reflector IJ of Figure 1, an arrangcincntsuch as that'I shown in Figure.4` inayheused.' In this` c e the red-reflective.dichroic'reflectqr Iltis' a conv tional device arranged an inverted `rrialn'-ner in accordance with this invention. The" blue',-

reective dichroic reflector 4], however, consists of .a support 48 `having a thickness, which is equal substantially `to one-,half of thethickness of the reflector I4 and ,ablue-reflective,coating-Nimm@ on the surface of 'the supportwhich is adjacent to the blue .kinescope I2; In orderth'at. ,thelighlt paths from ,the-linescclmes Il, [2 `and I.3"`r`nayfbe equalized, in accordance With the present 'invenff tion, there also is provideda transparentoptical member, such `as a plate 5I, having `a vtliicl'ines equal substantially tofolle-half',Qfj thethiclinSSbf the support i4. The pute .5 1 is mounted in spaced relation tothe dichroic reflector Y.41. 19.61- tween it and theblue kinescope I2.` Thespacing between the plate 5| 'and the `dichrojic 'reflector .41 is not critical. As in previously described ein,- bodiments of the invention, all sur`f`aoes`y of the optical members I5, 48and `5I which are not coated `for colored light reection are treated for no nreflection.y 'A It Will'bse'n that the blue light from lthe kine: .Seppe l? ireyele e seth heylh'ihf'e' 'leillh in air-from the kinescope sce'n'fto the'reflectiye .coaticg llili es in me .empodimnt of `the 'inyection shown in Figure l1.A Furthermorgthe'fblue `light ltravl'els the `half thickness ,plate 5I4 and the ,full thickness vsupport I 4 once. A green light `hem the `kiheseope le else nevels through .the two half thieknessmembers M 5I and the 4full thickness A,support I5. The red light, as in the previous instance, travels through the full thickness support I5 twice. Thus, light from all of the kinescopes travels a total distance through the denser-than-air media equal f eubsiehhehy ,te

where le lhebihlelseeee ef .the .reilererlplitilsefl v9 in the example described in connection with Figure 2.

It has been found that a somewhat simplified embodiment of the `invention may be used in cases where perfect registration of the blue irnage with the red and green images through all viewing angles is not required. In this case, the red dichroic reflector I is arranged in the manner previously described. The blue dichroic reflector 52 is arranged in a conventional way. The support 53 of the blue dichroic reflector 52 has a thickness which is equal to that of the support I5 of the red dichroic reflector I4. The surface of the support 53 which is adjacent to the blue kinescope I2 is provided with a bluereilective coating 54.

It may be seen that the red light traverses the full thickness support I5 twice, as in the previously described embodiments of thev invention. Also, the green light from the kinescope I3 traverses the full thickness support 53 of reflector 52 and also the full thickness support I5 of reflector I4. Accordingly, there is substantially eX- act registration between the red and green irnages for all angles of view. The blue light, derived from the kinescopes I2, however, passes through only one thickness of a medium which is more dense than air, e. g. the support I5 of the red-refiective dichroic reflector I4. Accordingly, there is some mis-registration between the blue image and the red and green images at large viewing angles. However, in many cases, it is not objectionable since the acuity of the average observer for the blue image is somewhat less than for the red and green images.

A somewhat different embodiment of the invention is disclosed in Figure 6 to which reference now will be made. This form of the invention is another color television image-reproducing system which may be directly viewed. The red, blue and green kinescopes Il, I2 and I5 are arranged substantially in the same manner as in the forms of the invention shown in Figures 1, 4 and 5. The color-selective optical system for combining the images produced by the kinescopes comprises dichroic reecting elements 55 and 56. The dichroic reflector 55 is arranged to receive red light from one direction and blue and green light from another direction and to direct it toward an observer. The dichroic reflector 56 is arranged to receive blue and green light from different directions and to direct it toward the dichroic reflector 55.

The dichroic reflector 55 is provided with a color-selective layer 51 mounted between two transparent optical members constituting supports 58 and 59. The color-selective layer 5l is capable of reflecting blue and green light and of transmitting red light. The thickness of the support 59 should be substantially equal to onethird of that of the support of 58. Using the same parameters referred to in other forms of the invention described, the thickness of the support 59 is and the thickness of the support 58 is making the total over-all thickness of the dichroic reflector 55 equal to 2T.

The dichroic reflector 56 is of the same gen- ,eral type as the dichroic reflector l1 of Figure 1.

It comprises a color-selective layer 6I which is capable of reflecting blue light and of transmitting green light. The color-selective layer is mounted between two transparent optical members forming supports 62 and 63. In this form of the invention, the color-selective layer is mounted substantially equidistant from the outside surfaces of the supports. Also, the thickness of each of the supports 62 and 63 is equal to in which case the total over-all thickness of the dichroic reiiector 56 is equal substantially to T.

The embodiment of the invention shown in Figure 6 operates in a slightly different manner from any of the previously described embodiments. Blue light from the kinescope I2 is reilected by the dichroic element 56 and is directed upwardly in combination with the green light derived from the kinescope I3. The green light is transmitted by this dichroic element in substantially exact register with the blue light. The combined blue and green images then are reflected by the dichroic element 55 in substantially exact optical register with the red image derived from the kinescope Il. The composite color television image may be viewed by looking directly at the dichroic reflector 55.

It will be noted that, in this form of the invention, there is no need for a plane mirror such as the mirror 2i of Figures 1, 3, 4, and 5. It will be appreciated that this mirror also may be omitted from the forms of the invention shown in these other figures if desired. The purpose of a reflector of this type is to enable viewing of the picture from a more suitable angle which will enable the achievement of a more compact mechanical design of the equipment. It will be understood, therefore, that in the other forms of the invention previously described the plane reflector or mirror may be omitted if desired.

It may be seen from the relative dimensions of the dichroic reflectors 55 and 5t given in the cos B where B is the angle made by the light path with a normal to the surface of the supports 58 and 59. In a like manner, it is seen that the length of the blue light path in the dichroic reflector 56 is equal substantially to cos B by twice traversing the support 62. Similarly, the blue light path in the dichroic reflector 55 includes two traversals of the support 59 and,` therefore, is equal substantially to cos B Accordingly, the total length of the blue light cos B the saine as the length ofthe red iight 'throughthe dichroic `,reflector 55. i

, greenli Aht path tranverses the supports a'd '63 bf dichroic reflector 56. Consequently,

the length of this path through this element 'is equal substantially to cos B fseiiuatthe length of the u ght paths ofthe different component color 'images all are substanatea tially equal throughthe denser-thariA-air lmedia comprising l.the dichroic re'ectorfsupports. As other, forms .of fthe, invention,` the hinescopes l,l, l2L and lk3are assumed to be suitablyl spaced from ,thedichroic reflectors 55 and 56 so that thereissubstantial equality inthe length of the lighltpaths `through air from the respective light souresto-the observer. Accordingly, the system embodiesthe underlying `principles of this invention, ,whereby to effect substantially exact optigalsregistration of the plurality of component eoletimegee.-

.The foregoingdisclosure of several representa ve embodiments of the invention demonstratesthel underlying principles of` the inven- ItV now may be seen that an'arrangement ettrieoliehreigreileetere 1*elettive "ee the diierentlyoloredlight sources and to'an observer proesehtpeeue Whiehereellef the Seme length agdwhicharqall ofthe same character with retofthesdiffferent, lint-dita traversed by lthe i 1 i811l1- )Theireslt isf aeheved Pifafmngfgf the rellene ve eeetines ef;the diehreieeeetefe ,in etenswaren@ the light te Pe releeied traverses the transparent support for substantially the same distance as the light which is to be transe mitted by the reflector.

Modifications of the invention other than the llustratively. disclosed embodiments.thereof4 will occurtdthoseskilled in the art. The scope of thejnventionembodying the. foregoing principles islset 4forthin th'efollowirig claims.

What is claimed is: i

1. In a color-selective optical system for combining images derived from a plurality of sources of light of different colo'rs'ydichroic reflecting apparatus disposed to receive from different directipnsj light froinitwo of saidsources,saiddicliroic apparatus.. including, a .color-selective Iayeraof. .a material capable of transmitting light oiat` least one particular oneofjsaid colors and of reflecting lig-ht of at least another particular one of said colors, and a transparent optical member capable of transmitting substantially indiscriminately lightW of both of said particularl colors and having color-selective layer and the source of light retot r... L Zmyrqm wwglf. o.' cted by said layer, whereby light said particulari colors caused to traverse s'ad transparent Optiaflmimbls 2- Diehreie renewing appaeiueee de claim `wherein.. seid eelerrseleeiive. leren and Seid eetieeimembe? term. e imiter! Strueturem i Diehroie-reeetins apparatus es' slefned in Glim 1i Wllen. Seid CQlOr'SQleclY ylj posed in spaced relation to both surfaces of said 0Dtiea1- member 4- Diehroimeeetins apueretuescl. .11.111 elem 1, wherein said color-Selective. laverie dieposedpn a Surface. of seidoptical member.. 5, Dichroic refiecting I apparatus Yas, Vdefnedwin claim 1, wherein said colorselective,layerjis sep: arated ,from both of said light sources by said optical member. A6. In a colorfselective, ,optical system'. Issuedtive sources of lightlof two dliferent colors, and a `dichroic reflector ,disposed to receive ,fromA different directions lightfrojrn` saidrespec tive sources, ,said .reflector comprising a supporter a transparent material capable of transmitting substantially indiscriminately `light [of bothY of said colors, and @color-selective layerofa ma,- terial capable of transmitting'light o f one'of said colors andof reflecting light of theuotherof said colors, said color-selective layerA 'beingisposed on said support in spaced relation to thatsurface of said support which 'sadjacentto said source .0f reflected light, whereby 1ight 0fboth of said colors is caused to traversesaid transparent supporto 7. In a color-sensitive opticalsystem defined in "claim 6, adichroicreflector wherein said colorsensitive layer ison that surface "of said support whlilch is adjacent to said source of transmitted lie 8. `In a colorrisensitive optical system as dened in claim 6a dichroic reflectorgwhereins'aid colorsensitivelayer ismoun'ted between both outside surfaces of said support. i

9. In a color-sensitive optical jsystem as defined inclaim 6, a dichroic reflector wherein said color-,sensitive layer is, mountedbetween and, substantially. .equidistant from, both outside surfaces of saidsupp'ort. 10. In acolor-sensi'tive opticalmsystexnasdefined in claim 6.,.a ,dichroic reflector wherein said color-sensitive layer is mounted` between both `outside surfacesof said 'supportandcloser `to one than to the other of. .said outside surfaces.

11.111,21,n color-sensitive optical system asdefined Claim 6Ia dichrdlc refiectorwherein said color-,sensitive 1ayer is mounted, between, both outside surfaces of said support and at a"dlstance 'from one. oi saidsurfaces which equalsubstantiallytoonehird of its distance from the other ofsad surfaces. y

12, In a co1or te,1evision system .includingreerectil/oscurece@,a plurality emitieron; cemponent eelorfimasesodi hrocrefieetius apparatus for combining said images in substantially exact registration, sadl` dichroic reflecting apparatus comprising a rls't dichroic reflecting ele ment disposed to receive two of said component color images v'from different. directions; "a 'second dichroic refiecting element disposed to receive a combination of said two `component color images from said first reflecting element; and a third component color iiri'ag'efrom athiid oiiejcf Said sources, each of said dichroic reflecting 'elements including ja color-'sensitive 'I'yer "ofra" material capable o'ftrrrsniit'ung ligrtf participar-'otre or a combination of two or more of said colors and of reflecting light of another particular one or a combination of two or more of said colors, and a transparent optical member capable of transmitting substantially indiscriminately light of any of said colors, said optical member in at least one of said dichroic reflecting elements being located between said color-selective layer and the source of image lightl to be reflected by said layer, whereby both the light which is reflected and the light which is transmitted by said dichroic reflecting element are caused to traverse said transparent optical member.

13. In a color television system as defined in claim 12, dichroic reflecting apparatus wherein both of said dichroic reflecting elements have the transparent optical members located between the respective color-selective layers and the respective sources of component color images reflected by said layers.

14. In a color television system as defined in claim 12, dichroic reflecting apparatus wherein one of said dichroic reflecting elements has the color-sensitive layer disposed on that surface of said transparent optical member which is adjacent to the source of the component color image to be transmitted by said dichroic reflecting element, and another one of said dichroic reflecting elements has the color-sensitive layer mounted between the two outside surfaces of said transparent optical member.

15. In a color television system as defined in claim 12, dichroic reflecting apparatus wherein said ilrst and second dichroic reflecting elements have the respective color-sensitive layers mounted between the two outside surfaces of the associated transparent optical members.

16. In a color television system in accordance with claim 12, dichroic reflecting apparatus wherein one of said dichroic reflecting elements has the color-sensitive layer mounted on the surface of said transparent optical member which is adjacent to the source of the component color image to be transmitted and the other of said dichroic reflecting elements has the color-sensitive layer mounted on that surface of an additional transparent optical member which is remote from the source of the component color image to be transmitted, and in which said first-mentioned transparent optical member is mounted in spaced relation to its associated colorsensitive layer on the side thereof adjacent to the source of component color image to be reflected by said layer.

17. In a color television system in accordance with claim 12, dichroic reflecting apparatus wherein the color-sensitive layers are mounted respectively on outside surfaces of said transparent optical members, said rst dichroic refleeting member having the color-sensitive layer on that surface of its associated transparent optical member which is remote from the source of the component color image to be transmitted, and the color-sensitive layer of said second dichroic reflecting elementbeing on that surface of its associated transparent optical member which is remote from the source of the component color image to be reflected.

18. In a color television system in accordance with claim 12, dichroic reflecting apparatus wherein one of said dichroic reflecting elements has the color-sensitive layer mounted between and substantially equidistant from both outside surfaces of its associated transparent optical members and is capable of reflecting one of said component color images and of transmitting another of said component color images, and the other of said dichroic reflecting elements has the color-sensitive layer mounted between both outside surfaces of its associated transparent optical member at a distance from that surface which is adjacent to said one dichroic reflecting element which is equal substantially to one-third of the distance from the other of said surfaces and is capable of reflecting Aboth lcomponent color images received from said one dichroic reflecting element and of transmitting a third one of said component color images.

19. In a color-selective optical system for color television reproduction by three kinescopes operative respectively to produce red, blue and green component color television images, component color image-combining apparatus including a dichroic reflector comprising a support of a material capable of transmitting without substantial discrimination light of all of said component colors and a color-selective layer of a material capable of transmitting blue and green light and of reflecting red light, said red-reflective layer being disposed on the surface of said support which is remote from said red image-producing kinescope, a second dichroic reflector disposed in spaced relationship with said ilrst reflector and in position to receive on the opposite surfaces thereof blue and green light respectively from said blue and green image-producing kinescopes, said second reflector comprising two elements capable of transmitting without substantial discrimination blue and green light and a layer of a material capable of transmitting green light and of reflecting blue light mounted intermediate of adjacent surfaces of said light transmitting elements, both of said dichroic reflectors being disposed relative to one another and to the respective kinescopes in a manner, whereby light of all colors follow paths of substantially equal length and include substantially the same character of media.

J ANCE-S E. ALBRIGHT.

References Cited in the file of this patent UNITED STATES PATENTS Number 

